in assessment of macular diseases
using high-definition
spectral-domain optical coherence
tomography
Inaugural-Dissertation
zur Erlangung des Doktorgrades
der Medizin
der Medizinischen Fakultät
der Eberhard Karls Universität
zu Tübingen
vorgelegt von
Treviño Rodríguez, Hugo
Alejandro
Dekan: Professor Dr. B. Autenrieth
Berichterstatter: Professor Dr. F. Gelisken
To my parents:
Who gave me a wonderful life, and all the support and opportunities.
To my wife, Krystal:
Who has taught me how to be a better human being, who has beared with me for so many years, and has shared the good and the bad.
To my children, Julia and Aidan:
Who have taught me how much my parents love me, and for all the happiness
Contents
Abbreviations
1. Introduction 1
1.1 Overview of the Macula 3 1.2 Retinal structures 5 1.3 History of Optical Coherence
Tomography (OCT) 7
1.4 Principles of OCT 9 1.5 Time-domain OCT (TD-OCT) 10 1.6 Limitations of TD-OCT 13 1.7 Spectral/Fourier-domain OCT (SD-OCT) 14 1.8 Limitations of SD-OCT 15 1.9 Advantages of SD-OCT 15 1.10 Spectralis OCT 17
1.11 OCT characteristics in Macula 18 1.12 OCT findings in Macular
Diseases 20
1.13 Pattern of OCT in Retinal Vascular Diseases 22 1.13.1 OCT in Diabetic Macular
Edema (DME) 22
1.13.2 OCT in Branch Retinal Vein Occlusion (BRVO) 25 1.13.3 OCT in Central Retinal
Vein Occlusion (CRVO) 27 1.13.4 Principles of the treatment
of Retinal Vascular
1.14 OCT in Vitreoretinal Interface Disorders 29 1.14.1 Vitreomacular Traction Syndrome (VMTS) 29 1.14.2 Epiretinal Membrane (ERM) 31
1.14.3 OCT in Macular Holes 33 1.15 OCT in Age-Related Macular
Degeneration (ARMD) 37 1.15.1 Non-neovascular ARMD 38 1.15.2 Neovascular ARMD 42 1.15.3 Treatment of ARMD 45 1.16 Anti-VEGF treatments 46 1.16.1 Ranibizumab (Lucentis) 47 1.16.2 Bevacizumab (Avastin) 48 1.16.3 Pegaptanib (Macugen) 49 1.16.4 Aflibercept (Eylea) 49
2. Material and Methods 50 2.1 General objective 50 2.2 Hypothesis 50 2.3 Definitions 51 2.4 Study population 51 2.5 Inclusion criteria 52 2.6 Exclusion criteria 53 2.7 Selection of the study
population 53
2.8 Design 54
2.9 Design description 54
2.10 Sample size 55
2.11.1 Ophthalmologic
examination 56
2.12 Examination protocol of
the OCT 57
2.12.1 Preparation of the patient 57 2.12.2 Preparation of the OCT 57 2.12.3 Settings of Spectralis OCT 58 2.13 Artifacts and Gradability of the
images 61
2.14 Color fundus photography,
Fluorescein angiography and Indocyanine green angiography 61
2.15 Data analysis 62 2.16 Variables 66 2.17 Statistical analysis 68 2.18 Description of activities 69 3. Results 70 3.1 Demographic data 70 3.2 Results of CRT in macular diseases 72 3.3 Intraobserver agreement in macular diseases (HT1-HT2) 72 3.4 Interobserver agreement in
macular diseases: first analysis
(HT1-ML3) 73
3.5 Interobserver agreement in macular diseases: second analysis (HT2-ML3) 74 3.6 Results of morphological
3.7 Total results of morphological findings 85 3.8 Results of nongradable morphological findings 87 4. Discussion 89 5. Summary 98 6. Bibliography 102 7. Deutsche Zusammenfassung 130 8. Acknowledgements 134 9. Curriculum vitae 137
List of Charts Page
1. Central retinal thickness between
intraobserver in macular diseases 76 2. Central retinal thickness between
interobserver in macular diseases:
first analysis 77
3. Central retinal thickness between interobserver in macular diseases:
second analysis 78
List of Tables
1. Demographics data of patients with
macular diseases 70
2. Gradability of OCT- images by
observers in macular diseases 71 3. Intraobserver agreement in macular
diseases 73
4. Interobserver agreement in macular
diseases: first analysis 74 5. Interobserver agreement in macular
diseases: second analysis 75 6. Result of Foveal depression (Fo_De) 79
8. Result of Vitreofoveal traction (VFT) 80 9. Result of Pseudocyst 80 10. Result of Splitting 81 11. Result of Verticalisation 81 12. Result of Macular hole (MH) 82 13. Result of Pseudomacular hole (PSM) 82 14. Result of Lamellar macular hole (LMH) 82 15. Result of Neurosensory detachment
(NSD) 83
16. Result of Pigment epithelium
detachment (PED) 83
17. Result of External limiting membrane
(ELM) 84
18. Result of Photoreceptors inner and outer segments (IS/OS) 84 19. Degree of agreement in morphological
findings 86
Abbreviations
ARMD Age-related macular degeneration A-SCAN Axial scan
BRVO Branch retinal vein occlusion CC Coefficient correlation
CI Confidence interval
CNV Choroidal neovascularization CME Cystic macular edema
CRVO Central retinal vein occlusion CRT Central retinal thickness DM Diabetes mellitus
DME Diabetic macular edema DR Diabetic retinopathy
ELM External limiting membrane ERM Epiretinal membrane
ETDRS Early treatment of diabetic retinopathy study
FAZ Foveal avascular zone
FIG Figure
GA Geographic atrophy GCL Ganglion cell layer INL Inner nuclear layer
ILM Internal limiting membrane IMH Idiopathic macular hole IPL Inner plexiform layer
IS/OS Inner and outer segment junction LMH Lamellar macular hole
MD Mean difference
ME Macular edema
MH Macular hole
NSD Neurosensory detachment of the retina OCT Optical coherence tomography
ONL Outer nuclear layer OPL Outer plexiform layer
PDR Proliferative diabetic retinopathy PDT Photodynamic therapy
PSM Pseudomacular hole
PVD Posterior vitreous detachment RNFL Retinal nerve fiber layer RPE Retinal pigment epithelium
SD-OCT Spectral domain optical coherence tomography
TD-OCT Time domain optical coherence tomography
VEGF Vascular endothelial growth factor VFT Vitreofoveal traction
1. Introduction
The macula is a round highly pigmented yellow spot at the center of the posterior pole, it specialized for high acuity vision and it is important for reading, writing, driving, working on the computer and for trips (American Academy of ophthalmology, 2011).
Macular edema (ME) is the most common pathology of the macula, which is the main cause of impairment of central vision. Diseases such as diabetic macular edema (DME), age-related macular degeneration (ARMD) retinal vascular occlusive diseases, and vitreoretinal interface disorders are the most frequent reasons of ME. For more than 30 years, physicians have been trying to identify the macular edema in its initial state and to define their different etiologies (Nussenblat RB et al., 1987).
Since 2004, the clinical diagnosis of macular diseases and its treatment have been greatly improved due to remarkable advances of modern imaging technologies, such as Spectralis optical coherence tomography (OCT) that has a valuable technique for the detection, evaluation and monitoring the central retinal thickness measurement (CRT) in macular diseases (Wotjkowski M, Srinivasan et al., 2005; Alam S, Zawadzki RJ, Choi S, et al., 2006).
One of the most important innovations in the field of macular diseases has been the introduction of intravitreal drug delivery approaches for the treatment of posterior segment pathologies. These emerging modalities restore the permeability of the blood-retinal barrier by delivering drug compounds intravitreally with anti-inflammatory or anti-vascular endothelial growth factor drugs (Anti-VEGF).
Even though the morphological findings of the macular pathologies are known, the interpretation and measurements of them by OCT may vary. Some of these factors are; the quality of the captured images, the type of the OCT machine, the experience of the physician and at lastly the complexity of the findings.
The purpose of this study is to determine the degree of agreement between a general ophthalmologist and a retina specialist in the diagnosis and classification of the CRT and morphological findings found by Spectralis OCT in macular diseases. The reliability between the observers and intraobserver will be analyzed by statistical methods.
1.1 Overview of the Macula
The macula also called (macula lutea) is a round highly pigmented yellow spot at the posterior pole, lying inside the temporal vascular arcades; it has a diameter around 5 and 6mm, and subserves the central 15–20° of the visual field. This area contains a retinal pigment xanthophyll that confers hypofluorescence on angiography.
The macular area is centered on the fovea, a small concave depression retinal about 1.5 mm in diameter where the photoreceptor layer is formed exclusively by cones which constitute 10% of the retinal cones. The foveal cones are specialized and have an especially high density.
In the center of the fovea, there is the foveola, which is an avascular zone irrigated by the choriocapillaris. This part of the fovea does not contain inner nuclear layer and ganglion cell layer. The parafoveal area is a ring that is located 0.5 mm around the fovea. It is a region where the retina is thicker. The perifoveal area is a ring of 1.5 mm in diameter around the parafovea.
In the fovea there are 35,000 cones connecting with ganglion cells, so which is the area with the greatest capacity for visual discrimination of the retina
(American Academy of ophthalmology, 2011) (Fig. 1).
Fig. 1: Color photograph of the posterior pole. The anatomical fovea and foveola are in the center of the anatomical macula (by Spaide R.F. 2011).
1.2 Retinal Structures
The retina is composed of ten distinct layers. These layers are dark nuclear layers, containing cell bodies, or light plexiform layers, containing axons and dendrites (Fig. 2).
Fig. 2: Histological representation of the layers of the retina (by University of Bristol, Department of Anatomy 2000).
The retina is a highly organized structure with common-path neuronal axons of ganglion cells, which leads the visual information to the brain. It has an average of 4.6 million cones and 92 million rods (American Academy of ophthalmology, 2011).
The Internal limiting membrane (ILM) is the most superficial layer of the retina and is in contact with
the hyaloid of the vitreous gel. Histopathologically consists of the basement membrane of the extensions of the Müller cells. In the parafoveal and peripapillary region, the thickness of the ILM is about 2.5 microns. The side facing the vitreous cavity is thin, and the inside or retinal face is polished and irregular.
The ILM can act as a basis for cell growth and proliferation. Frequently involved in disorders that affect the vitreomacular interface, including epiretinal membranes (ERM), vitreomacular traction syndrome (VMTS) and macular hole (MH).
The inner third of the outer plexiform layer has a linear density where a synaptic connection between the photoreceptors and the processes of the bipolar cells occurs.
The retinal pigment epithelium (RPE) is composed of a single layer of hexagonally shape cuboidal cells, lying between Bruch’s membrane and retina. These cells and the zonula occludentes constitute the outer blood retinal barrier, preventing extracellular fluid leaking into the subretinal space from the choriocapillaris, actively pump ions and water out of the subretinal space.
The central retinal artery and its branches, as well as the derivative venous return, are located in the inner retina, supplying nutrition to the inner nuclear layer. The nutritional value of the outer retina depends on the choriocapillaris, which is the innermost layer of the choroid that provides irrigation to the choroidal circulation.
The vitreous cavity has a capacity of about 3-4 ml, which is 4/5 of the volume of the eyeball. The vitreous gel is tightly attached to the retina in the vitreous base, which extends to about 2-3 mm to the ora serrata.
The posterior hyaloid is strongly attached to the optic nerve, retinal vessels, macula and some retinal scars (Yanoff M, Duker JS, 2008; American Academy of ophthalmology, 2011).
1.3 History of Optical Coherence Tomography (OCT)
In 1991, OCT was described by Huang and associates, as a non-invasive medical diagnostic imaging, which performs micrometer resolution cross-sectional or tomographic imaging of the tissue using low coherence interferometry (Huang D, Swanson EA, Lin CP et al. 1991).
In 1993, the first in vivo OCT-images (displaying retinal structures) were published (Fercher AF., Hitzenberger CK, Drexler W et al., 1993; Hee MR, Swanson EA, Izatt J et al., 1993).
In 1995, time-domain optical coherence tomography (TD-OCT) was used for imaging macular diseases. Since then, OCT has become widely accepted for retinal thickness measurements and detection of the macular morphology in various retinal diseases (Puliafito CA, Hee MR, Lin CP et al., 1995).
In 2002, TD-OCT 300 (Stratus OCT) became available with an axial resolution of 10 µm and a scan velocity of 400 axial scans per second (Drexler W, Sattmann H et al., 2003).
Since 2004, higher-resolution spectral-domain OCT (SD-OCT) has entered clinical practice with reported resolutions of 1 to 5 µm as well as improved visualization of retinal morphologic and pathologic features. Today it is the current “gold standard” for posterior segment retinal tomography (Drexler W, Sattmann H et al., 2003; Wotjkowski M, Srinivasan et al., 2005; Alam S, Zawadzki RJ, Choi S et al., 2006).
1.4 Principles of OCT
OCT is analogous to B-mode ultrasound, except that uses light rather that wave sound. Unlike ultrasound, OCT does not require contact with the tissue examined. OCT is based on an apical measurement technique known as a low coherence interferometry, which can be used to measure ocular structures with high precision by measuring the light reflected from them (Huang D, Swanson EA, Lin CP et al., 1991).
In the OCT, a beam of light from a superluminescent diode is divided through a beam splitter into sample and reference beams (Fig. 3). Light from the sample beam is directed toward the tissue of interest. The light will be reflected with different echo time delays. Light from the reference beam is reflected from a different mirror located at a known distance. Both the reflected reference and sample beams are combined by a modified Michelson interferometer and detected by the OCT
(Huang D, Swanson EA. Lin CP et al., 1991; Hee MR, Izatt JA, Swanson EA et al., 1995).
Detection of these beams is based on time-domain or spectral-domain protocols.
Fig.3: Principle of a Michelson interferometer type OCT system (by Jansz 2012).
1.5 Time-domain OCT (TD-OCT)
In TD-OCT, the position of the reference mirror is adjusted, creating different time delays for the echoes of the reference beam. Axial scans (A- scan) are obtained by directing the sample beam at different tissue depths and recording the reflected light echoes (Hee MR, Puliafito CA et al., 1995).
An example of TD-OCT is the Stratus-OCT, which has a resolution of <10 µm and can make from 128 to 768 A-scan in a single scan pass. Each A-scan has 1,024 data points and is 2mm long. By scanning the sample beam of light in a transverse direction, a cross sectional OCT (B-scan) image is obtained. Once the information has been obtained, a tomography is constructed using a false color scale that represents the amount of light backscattering from microstructures at different depths of the imaged tissue.
The images in TD-OCT are displayed in false color scale, bright colors such as red to white represent high reflectivity and dark colors such a blue to black represent minimal or no reflectivity (Hee MR, Puliafito CA et al., 1995) (Fig. 4).
The ganglion cell layers (GCL), the inner nuclear layer (INL) and the outer nuclear layer (ONL) have a low reflectivity, and therefore appear blue-black in the false color scale. Conversely, the retinal pigment epithelium (RPE)/choriocapillaris and the retinal nerve fiber layer (RNFL), exhibit a high reflectivity
(Toth CA, 1997).
The hyper-reflective band at the level of the RPE/choriocapillaris is actually composed of two highly reflective lines separated from each other by
one thin layer of low to moderate reflectivity. The inner highly reflective line corresponds to the junction of the photoreceptor´s outer and inner segments (IS/OS). The outer highly reflective line corresponds to the RPE/choriocapillaris. Traditionally, the inner and outer retinal boundaries have been defined as the INL and RPE respectively
(Costa RA et al., 2004; Pons ME et al., 2005; Sadda SR et al., 2007) (Fig. 4).
Fig. 4: The time-domain Stratus OCT, the images are displayed in false color. High reflectivity structures are depicted as red, intermediate as green-yellow and low reflectivity as blue-black. High resolution OCT (B) has the ability to identify fine retinal structures such as the external limiting membrane and ganglion cell layer which
are not visualized as clearly with standard resolution (A). NFL: Nerve fiber layer, GCL: Ganglion cell layer, IPL: Inner plexiform layer, INL: Inner nuclear layer, OPL: Outer plexiform layer, ONL: Outer nuclear layer, ELM: External limiting membrane, IS/OS: Inner segment/outer segment junction, RPE: Retinal pigment epithelium (by Kanski J. 2011).
1.6 Limitations of TD-OCT
EA Swanson et al. mentioned that although the time domain Stratus OCT achieved high resolution images of the eye; the image quality was limited by the speed of image acquisition (Fig. 4). Also mentioned that in each successive axial scan, the axial movement of the eyes of the patients became increasingly important in the quality and precision of the image factor. After image acquisition, digital processing could eliminate axial movement artifacts, however, it could also introduce errors in the topography of the retina (Swanson EA, Izatt JA, He MR et al., 1993). Image acquisition speed also limited the total
number of cross-sectional images. The movement of the eyes, dry tear film and blinking were contributing to poor quality images with higher image acquisition time. As a result, the TD-OCT retina coverage was limited. Focal pathologies could not be detected in a B-scan determined by OCT, leading to sampling errors. Moreover, since the
OCT B-scan was limited (Ray R, Stinnet SS, Jaffe GJ, 2005; Sadda SR et al., 2006).
1.7 Spectral/Fourier–domain OCT (SD-OCT)
SD-OCT detection represents an advance in OCT technology that enables imaging speeds of >25,000 axial scans per second, or 50 times faster than TD-OCT. Spectral or Fourier domain OCT is so named
because the interference spectrum of echo time delays of light is measured by a spectrometer and high-speed charged-coupled device camera (Fercher AF et al., 1995; Wojtkowski M et al., 2002; Nassif NA et al., 2004; Leitgeb RA et al., 2004; Srinivasan J et al., 2006).
Because the interference spectrum is composed of oscillations whose frequencies are proportional to the echo time delay, axial scan measurements can be obtained by calculating the Fourier transform. (A Fourier transform is a mathematical operation that extracts the frequency content of a signal). In contrast to TD detection, SD detection measures all echoes of light simultaneously, and the position of the reference arm does not need to be adjusted. The result is a significant improvement over time-domain OCT in sensitivity and image acquisition speed (Chen TC, Cense B, 2005)(Fig. 5).
Fig.5: Multiple spectral/Fourier–domain OCT. Note the spectrometer
and the Fourier transform in SD-OCT (by Graf 2009).
1.8 Limitations of SD-OCT
The disadvantage of spectral/Fourier domain detection is that detection sensitivity and image resolution depend on imaging depth because of limitations on spectrometer resolution.
1.9 Advantages of SD-OCT
One of the main advantages of the SD-OCT is that with the increase in speed of image acquisition, motion artifacts are minimized, resulting in images
of higher quality and finer discrimination of intraretinal layers. SD-OCT has the ability to acquire a large number of cross-sectional images quickly to improve the coverage of the retina and also has the ability to allow multiple scan OCT cross sections to be taken on in a pattern of dense plot to cover a large area of the retina (Fig. 6).
Fig.6: Comparison of TD to SD-OCT images. A normal macular scan acquired with SD-OCT (A). The same eye scanned with TD-OCT (B). Note the clear delineation of each retinal layer and the ability to clearly distinguish the inner segment/ outer segment junction of the photoreceptors from the retinal pigment epithelium in SD-OCT scans. NFL: Nerve fiber layer, GCL: Ganglion cell layer, IPL: Inner plexiform layer, INL: Inner nuclear layer, OPL: Outer plexiform layer, ONL: Outer nuclear layer, ELM: External limiting membrane, IS/OS: Inner segment/outer segment junction, RPE: Retinal pigment epithelium (by Yaqoob 2005).
1.10 Spectralis OCT
Spectralis OCT (Heidelberg Engineering, Heidelberg, Germany), is the newer SD-OCT that uses a significantly faster, non-mechanical technology.
Spectralis OCT measures simultaneously multiple wavelengths of reflected light across a spectrum, hence the name spectral domain. The system is 100 times faster than TD-OCT and acquires 40,000 A-scans per second with 5 µm optical, 3.9 µm digital axial resolution and 1.9mm scan depth. The increased speed and number of scans translates into higher resolution and a better chance of observing the diseases (Han IC, Jaffe GJ, 2009; Wolf-Schnurrbusch et al., 2009) (Fig. 7).
High speed image acquisition is combined with custom TruTrack technology to actively track the eye during imaging. Tracking eye movement with simultaneous dual-beam imaging minimizes motion artifact, enables noise reduction and allows the instrument to precisely track change over time. This real-time eye tracking enables a highly repeatable alignment of OCT and fundus images that can be displayed either in grayscale or false color and allows acquisition of 1 to 100 B-scans at the same location, facilitating removal of speckle noise artifact. The result is point to point correlation
between the fundus and OCT scans, greater image detail and clarity, and more confident assessment of small changes (Wolf-Schnurrbusch et al., 2009).
Fig. 7: Example of a normal eye image with the Spectralis OCT high resolution. (ILM: internal limiting membrane; NFL: nerve fiber layer; GCL: ganglion cell layer; IPL: inner plexiform layer; INL: inner nuclear layer; OPL: outer plexiform layer; ONL: outer nuclear layer; ELM: external limiting membrane; IS/OS: photoreceptor inner/outer segment junction; RPE: retinal pigment epithelium, BM: Bruch membrane).
1.11 OCT characteristics in Macula
The OCT-image closely approximates the histological appearance of the macula and, for this reason, it has been referred to as an in vivo optical biopsy. When light travels through the retinal tissue it can be reflected, scattered, or absorbed, and this creates the multilayered pattern of the retina (Drexler W, Fujimoto JG, 2008).
The first detected layer in most OCT scans is the ILM that appears as a hyper-reflective layer at the vitreoretinal interface. Occasionally, the posterior hyaloid can be seen above the ILM as a hyper-reflective layer. Within the retina, the RNFL, IPL and OPL are seen as hyper-reflective while the GCL and the nuclear layers are hypo-reflective. The retinal vessels may sometimes be seen on OCT images as circular hyper-reflective structures located in the inner retina, with a vertical shadow or reduced reflectivity extending into deeper layers (Drexler W, Sattmann H, 2003, Schuman JS, Puliafito CA, 2004; Spaide RF, Curcio CA, 2011).
Outside the central fovea, SD-OCT instruments typically resolve four bands in the outer retina. The innermost band has been attributed to the ELM. This band is typically thinner and fainter than the others. The second of the four bands has been commonly described to the boundary between the IS/OS of the photoreceptors and the third band is referred to as Verhoeff’s membrane. The fourth hyper-reflective outer retinal band is attributed to the RPE, with potential contribution from Bruch’s membrane and choriocapillaris, with abundant experimental and clinical evidence supporting this designation (Zawadzki RJ, Jones SM et al., 2005; Alam S, Zawadzki RJ et al., 2006; Srinivasan VJ, Ko TH et al., 2006;
Srinivasan VJ, Monson BK et al., 2008; Spaide RF, Curcio CA, 2011)
(Fig. 8).
Fig. 8: (A) Example of a normal eye image with the Spectralis OCT high resolution. (B) Four hyper-reflective bands in the outer retina; ELM, IS/OS, Verhoeff’s membrane and the RPE/Bruch’s membrane complex. (NFL: nerve fiber layer; GCL: ganglion cell layer; IPL: inner plexiform layer; OPL: outer plexiform layer; ONL: outer nuclear layer; ELM: external limiting membrane; IS/OS: photoreceptor inner/outer segment junction; RPE: retinal pigment epithelium (by Ryan S. 2013).
1.12 OCT findings in Macular Diseases
Hard exudates are hyper-reflective lesions that look like hyper-reflective shades of neurosensory retina that completely block the reflections of the underlying retina. Thin hemorrhages are hyper-reflective, and if bleeding is thick, it can block the reflections of the underlying structures. Also epiretinal membrane (ERM), atrophy and all fibrotic lesions are hyper-reflective (Gupta V, 2004) (Fig. 9).
The hypo-reflective lesions are serous fluid that produces an optically empty space without
backscatter and pseudocysts characterized as a round or oval areas of low reflectivity in the layers of the retina (Gupta V, 2004) (Fig. 10).
Fig. 9: Spectralis OCT 5mm horizontal line scan passing through the foveal center. Note the pseudocyst (green arrow) as an oval area of low reflectivity. Also, note the presence of hyper-reflective band ERM (red arrow) and a macula atrophy (blue arrow).
Fig. 10: Spectralis OCT 5mm horizontal line scan passing through the foveal center. Note the presence of hypo-reflective lesions; pseudocyst (red arrow) subretinal fluid (green arrow) and diffuse retinal thickness (blue arrow).
1.13 Pattern of OCT in Retinal Vascular Diseases 1.13.1 OCT in Diabetic Macular Edema (DME)
For the management of diabetic maculopathy, OCT is an important tool for assessing retinal pathology, including retinal thickness, DME, intraretinal exudates, vitreomacular interface abnormalities, subretinal fluid, and photoreceptor IS/OS junction abnormalities. OCT is also important in monitoring the response to treatment of DME by laser, intravitreal pharmacotherapies, and vitreoretinal surgery.
DME can be associated with diffuse retinal thickening, cystoid macular edema (CME), serous retinal detachment or subretinal fluid, and vitreomacular interface abnormality (Otani T et al., 1999; Kim BY et al., 2006; Soliman W et al., 2008).
Diffuse retinal thickening is usually defined as a sponge-like swelling of the retina with a generalized, heterogeneous, mild hypo-reflectivity compared with normal retina. CME is characterized by the presence of intraretinal cystoids areas of low reflectivity, which are typically separated by highly reflective septa (Fig. 11). Serous retinal detachment is defined on OCT as a focal elevation of neurosensory retina overlying a hypo-reflective, dome-shaped space (Fig. 12). The posterior border
of the detached retina is usually highly reflective, which helps to differentiate subretinal from intraretinal fluid. Vitreomacular interface abnormalities include the presence of ERMs, VMT, or both (Otani T et al., 1999).
Fig. 11: Spectralis OCT 5mm horizontal line scan passing through the foveal center in an eye with DME. Note the large pseudocyst (yellow arrow), the sponge-like swelling of the retina (red arrow) and cystoid macular edema (green arrow) nasal to the fovea.
Fig. 12: Spectralis OCT 5mm verticall line scan passing through the foveal center in patient with DME. Note the presence of intraretinal cystoids areas of low reflectivity (red arrow), which are typically separated by highly reflective septa and a focal elevation of neurosensory retina overlying a hypo-reflective, dome-shaped space corresponding a serous retinal detachment (green arrow).
In the last decade, many agents like triamcinolone and anti-VEGF have been studied to treat DME. Michaelides M et al. mentioned that the OCT played an important role in determining the retinal thickness and the treatment response (Elman MJ et al., 2011; Michaelides M et al., 2010).Kim NR et al. reported that the
treatment responses of each OCT pattern of DME are different. Patients with diffuse retinal thickening may achieve a greater reduction in retinal thickness and a greater improvement in visual acuity compared with patients exhibiting CME, subretinal fluid, or vitreomacular interface abnormality (Kim NR et al., 2009; Soliman W et al., 2008).
Fibrovascular proliferation in Proliferative Diabetic Retinopathy (PDR) can be visualized with OCT imaging as highly reflective preretinal bands anterior to the retinal surface. Diffuse retinal thickening, distortion, and irregularity of the retinal contour can also occur as a result of the contraction of these preretinal membranes. An associated traction retinal detachment may be observed as well (Fig. 13).
OCT imaging is valuable in determining the extent of the tractional component as well as the presence of foveal involvement, assisting in the decision to intervene surgically (Haller JA et al., 2010).
Fig. 13: Spectralis OCT: 5mm vertical line scan through the macula in a patient with PDR. Note the highly reflective preretinal band anterior to the retinal surface (green arrow) and the diffuse retinal thickening (red arrow), distortion and the irregularity of the retinal contour.
1.13.2 OCT in Branch Retinal Vein Occlusion (BRVO)
BRVO is the second most common vascular disease of the retina after DR,it is usually caused by a thrombus at arteriovenous crossings where a thickened artery compresses the underlying venous wall (Duker JS, Brown GL, 1989).
BRVO is usually seen in elderly patients, between 60-70 years old; this pathology is associated with hypertension in 50 to 70% of the cases, cardiovascular disease, diabetes mellitus, and open-angle glaucoma (Duker JS, Brown GL, 1989; Spaide RF et al., 2003).
OCT findings include CME (Fig.14), serous retinal detachment, ERMs, pseudoholes, lamellar holes
(Fig.15), and subhyaloid or preretinal hemorrhages in BRVO. A significant proportion of patients with occlusion of the retinal venous system have OCT evidence of CME and serous retinal detachment (Ota M et al., 2008; Shroff D et al., 2008; Ryan S et al., 2013).
Fig. 14: Spectralis OCT 5mm horizontal line scan passing through the foveal center in patient with BRVO. Note the alteration in the foveal depression (red arrow) due to CME (green arrow) in an inferior-temporal retinal vein occlusion.
Fig. 15: BRVO associated with a lamellar macular hole, imaged by Spectralis OCT. Note the thin irregular foveal floor and split foveal edges (green arrow) accompanied with pseudocyst (red arrow).
1.13.3 OCT in Central Retinal Vein Occlusion (CRVO)
CRVO is usually caused by a thrombus in the area of the lamina cribrosa. It is associated with hypertension in 60% of patients. Usually seen in elderly patients over 50 years old and there is a slight male predilection (Hayreh SS, Zimmerman MB, 1994).
OCT plays a major role in studying macula in CRVO. In CRVO, the morphological findings visible in OCT include macular thickening, intraretinal cyst formation (Fig.16), lamellar macular holes, subretinal fluid accumulation, ERM and papilledema
(Catier A et al., 2005; Lerche RC et al., 2001; Ozdemir H et al., 2005).
The quantification of macular edema is demonstrated on OCT as a changes on the foveal depression, hypo-reflective areas of fluid accumulation and pseudocysts. Intraretinal hemorrhages appear as focal areas of bright and hyper-reflective backscattering which partially shadow the reflections from the retinal pigment epithelium and choriocapillaris (Ryan S et al., 2013).
Fig 16: Spectralis OCT image shows a macular thickening, intraretinal cyst formation (red arrow) with a hypo-reflective subretinal fluid accumulation (green arrow) in CRVO.
1.13.4 Principles of the treatment of Retinal Vascular Diseases
Focal laser photocoagulation reduces the risk of moderate visual acuity loss by 50% of the patients with DME and reserved for the noncenter involved edema. Other treatments modalities for DME include intravitreal injection of anti-VEGF drugs and corticosteroids. In case of associated vitreomacular traction is a macular surgery recommended.
The response to various treatments modalities for macular edema is variable. Some patients show excellent visual improvement whereas others show only minimal response. Therefore OCT plays a pivotal role in quantitatively monitoring changes in retinal thickness after treatment such as intravitreal corticosteroid and anti-VEGF injection or
photocoagulation (Greenberg PB, Martidis A, 2002; Martinez-Jardon CS, Meza-de Regil A, 2005).
1.14 OCT in Vitreoretinal Interface Disorders
Abnormalities of the vitreoretinal interface are involved in the pathogenesis of several macular conditions. In idiopathic epiretinal membranes (ERMs), a layer of fibrotic tissue develops on the surface of the retina, usually after a posterior vitreous detachment. Contraction of this membrane can result in retinal distortion, leading to vision loss. In other conditions, such as vitreomacular traction syndrome (VMTS) or idiopathic macular hole (IMH), there are abnormal attachments between the vitreous and the retina. The resulting traction exerted on the retina causes anatomical alteration and subsequent visual loss.
1.14.1 Vitreomacular traction syndrome (VMTS)
VMTS results from persistent vitreoretinal adhesions after the development of partial posterior vitreous detachment (PVD).In normal eyes, as the vitreous liquefies due to age, it detaches from the macula. This natural progression has been demonstrated using OCT (Uchino E et al., 2001). In some eyes, due to the strong adhesion between the vitreous and
macula, the vitreous detaches peripherally, and continues to pull on areas of the macula. The vitreoretinal adhesions transmit tractional forces to the retina from the vitreous body, having the potential to cause tensile deformation (Fig.17),
foveal cavitations, CME, limited macular detachment, or a macular hole (MH) (Schmiddy WE et al., 1989; Jhonson MW, 2005).
In recent years OCT has been most beneficial in diagnosing VMTS and subsequently directing treatment of this condition.
Sulkes DJ et al. mentioned that in some people spontaneous resolution can occur with separation of the vitreous from the macula, leading to subsequent resolution of the intraretinal and subretinal fluid and restoration of normal vision (Sulkes DJ et al. 2000).
However, in most eyes, VMTS may persist and intravitreal Ocriplasmin or vitrectomy may be an effective treatment option for patients with symptomatic VMTS. Consequently, OCT is useful in monitoring subtle changes in vitreoretinal adhesions and retinal architecture and assisting the treatment decision-making process (Yamada N, 2005; Witkin AJ et al. 2010).
Fig. 17: Spectralis OCT shows persistent vitreous adhesion at the foveola (green arrows) causing tractional foveolar thickening with cyst-like spaces (red arrow). This type of vitreofoveolar traction is a subtle variant of the vitreomacular traction syndrome.
1.14.2 Epiretinal membrane (ERM)
ERM occurs in approximately 6% of patients over the age of 60, with incidence increasing with age
(Mccarty DJ et al., 2005). ERMs are idiopathic or
secondary to an initiating event. Most idiopathic ERMs are thought to result from fibroglial proliferation on the inner surface of the retina secondary to a break in ILM occurring during PVD
(Smiddy WE, Maguire AM et al, 1989). Secondary ERMs
result from an already existing ocular pathology such as CRVO, BRVO, DR, uveitis, and retinal breaks with or without detachment (Appiah AP, Hirose T, 1989).
Glial cells, RPE cells, and myofibroblasts are shown to be mostly involved in ERM formation. (Smiddy WE, Maguire AM et al, 1989; Vinores SA et al.,1990). ERM may
lead to loss of normal retinal anatomy, with the patient experiencing metamorphopsia, micropsia,
monocular diplopia, and decreased visual acuity. These symptoms vary in severity depending on the location, density, and contraction of the membrane. Sometimes, ERMs can evolve into macular pseudoholes and ERMs are often seen in conjunction with idiopathic full-thickness macular holes (Schmiddy WE, Michels RG et al., 1990).
OCT provides qualitative and quantitative information about the retinal anatomy, which can identify factors contributing to vision loss in patients with ERM.
On OCT, ERMs are seen as a highly reflective layer on the inner retinal surface (Fig. 18). In most eyes, the membrane is globally adherent to the retina
(Fig. 19) but, in some cases, it can be separated
from the inner aspect of the retina, which enhances its visibility by OCT. In this situation, it is usually distinguishable from a detached posterior hyaloid. Secondary effects of the membrane include loss of the normal foveal contour, increased retinal thickness, and the presence of cystoids changes, and these features may be observed in more advanced membranes.
OCT is also useful for monitoring changes in cases that are being observed and for documenting the
response to treatment in patients undergoing pars plana vitrectomy with membrane peeling.
Fig. 18: Spectralis OCT shows the presence of hyper-reflective band (green arrow) at the vitreoretinal interface with traction on the underlying retina resulting in distortion of neurosensory retinal layers (red arrow).
Fig. 19: Spectralis OCT shows a hyper-reflective band corresponding an epiretinal membrane globally adherent to the retina and a loss of the foveal depression.
1.14.3 OCT in Macular Holes
Idiopathic macular holes (IMHs) typically occur in the sixth to seventh decade of life with a 2: 1 female preponderance. Symptoms include decreased
visual acuity, metamorphopsia, and central scotoma. Bilateral involvement occurs in 15–20% of patients.
A full-thickness defect in the neural retina as seen with OCT can differentiate a true macular hole from a pseudohole, lamellar macula hole, or a macular cyst. Lamellar macula holes show an increased foveal pit contour with a thin outer neurosensory retina (Fig. 20). Macular pseudoholes are seen in the presence of a dense ERM with a central defect that overlies the foveal center, giving the ophthalmoscopic appearance of a true macular hole
(Schumann JS, Puliafito CA, 2004) (Fig. 21).
Fig. 20: Main Spectralis OCT features shows a lamellar hole. Note the horizontal splitting of the foveal edges, irregularity of the foveal base and thinning of the outer neurosensory retina.
Fig. 21: Spectralis OCT features shows a pseudohole. Note the presence of a dense ERM (green arrows) with a steep configuration of the foveal edge (red arrow).
Gass described the stages of full-thickness MH formation based on biomicroscopic findings (Gass JD, 1995).
Stages 1 holes may be distinguished by a reduced or absent foveal pit and the presence of an optically clear space beneath the fovea, suggesting a foveolar detachment. Evidence of traction by the posterior hyaloid on the fovea may be present.
Stage 2 holes show a partial break in a surface of the retina with a small full-thickness loss of retinal tissue, <400 µm in size (Fig. 22).
Stage 3 holes have a full-thickness retinal dehiscence >400 µm in size with a complete break in the outer retinal tissue, and variable amounts of surrounding macular edema that increase retinal
thickness and decrease reflectivity in the outer retinal layers.
Stage 4 holes can be characterized by the complete loss of tissue >400 µm in size, and a complete detachment of the posterior vitreous (Fig. 23).
Stage 1 and 2 macular holes are very difficult to differentiate ophthalmoscopically and high resolution OCT images can help to classify them. Stage 2 often progresses to stage 3 with some visual loss; therefore, appropriate staging with OCT can help to determine when surgery is necessary
(Gass JD, 1990).
Pars plana vitrectomy with and without ILM peeling has become the standard treatment for macular hole with anatomical success rates of 85–100%
(Kelly NE, Wendy RT, 1991; Brooks HL JR, 2000). OCT can be used to confirm complete macular hole closure and restoration of the normal foveal contour.
Fig. 22: Spectralis OCT shows a stage 2 macular hole. A small full-thickness loss of retinal tissue, <400 µm in size.
Fig. 23: Spectralis OCT shows a stage 4 macular hole. A full-thickness retinal defect >400µm and a complete detachment of the posterior vitreous (green arrow).
1.15 OCT in Age-related macular degeneration (ARMD)
ARMD is a progressive degenerative disease of the retinal pigment epithelium, Bruch’s membrane, and choriocapillaris. It is classified in two forms: non-neovascular (dry) and non-neovascular (wet or exudative). The non-neovascular form accounts for 80–90% of cases while the neovascular form accounts for 10–20% of cases, but was responsible for the majority of severe vision loss (80–90%) prior to the widespread use of vascular endothelial growth factor (VEGF) inhibitors. Occasionally, the dry form can develop into the wet (Friedman DS et al., 2004; Klein R et al., 2004).
ARMD is the most common cause of central vision defects in the elderly in the Western countries over 50 years population (Klein et al. 1998; Age Related Eye Disease Study Research Group 2000), It is estimated that
approximately 30% of adults older than 75 years have some sign of ARMD and that approximately 10% of these patients have advanced stages of the disease.
Patients with advanced ARMD in one eye, or even moderate vision loss due to non-advanced ARMD in one eye, have about a 50% chance of developing advanced ARMD in the fellow eye within 5 years. Risk factors include increasing age (>75 years of age), positive family history, cigarette smoking, hyperopia, hypertension, hypercholesterolemia, female gender, and cardiovascular disease; nutritional factors and light toxicity also play a role in pathogenesis. There may also be a genetic component to ARMD(Hirvela H et al., 1996; Vingerling JR et al. 1996).
1.15.1 Non-neovascular ARMD
Non-neovascular (dry) ARMD is characterized by abnormalities of the RPE, Bruch’s membrane, and choriocapillaris. These abnormalities may be
asymptomatic or accompanied by compromised vision, and are considered to be the precursors of geographic atrophy (GA) and choroidal neovascularization (CNV) (Hirvela H et al., 1996; Vingerling JR et al. 1996).
Drusen appear clinically as focal white-yellow excrescences deep to the retina. They vary in number, size, shape, and distribution. The high-definition B-scans obtained with SD-OCT are useful to assess the ultrastructure of drusen and to evaluate for evidence of disruption of adjacent retinal layers (Fig. 24). Soft drusen are observed as focal elevations in the external, highly reflective band (RPE/choriocapillaris complex) consistent with the accumulation of amorphous material within or beneath Bruch’s membrane (Sikorski BL et al., 2010; Spaide R, Curcio CA 2010) (Fig. 25).
In larger drusen or drusenoid retinal pigment epithelial detachments (PEDs), the RPE has a greater elevation with a dome-shaped configuration
(Roquet W et al., 2004) (Fig. 26).
Larger drusen may often become confluent and can sometimes be accompanied by fluid accumulation under the retina in the absence of CNV (Sikorski BL et al., 2010). Recognition of this feature may avoid
Fig. 24: Spectralis OCT shows the presence of drusen (red arrow) as a focal elevation between the retinal pigment epithelium and membrane Bruch’s.
Fig. 25: Spectralis OCT shows the presence of large drusen (red arrow) and atrophy of the outer segments of the fovea (green arrow) in ARMD.
Fig. 26: Spectralis OCT shows a drusenoid RPE detachment (red arrow).
atrophy (GA) is seen clinically as one or more areas of hypopigmentation or depigmentation due to the absence of the underlying RPE. The deeper choroidal vessels are more readily visualized through the atrophic areas, and are accompanied by varying degrees of photoreceptor and choriocapillaris loss (Fig. 27). Associated retinal atrophy is seen as thinning or loss of the outer nuclear layer and the absence of ELM and IS/OS junctions (Fleckenstein M et al. 2008).The loss of
photoreceptors often extends beyond the margins of GA, with the ELM and IS/OS junctions disappearing while bridging across the GA margin. Evaluation of these junctional zones may provide information about the pathogenesis of GA, and the role of RPE, photoreceptor, and choriocapillaris loss in the initiation and propagation of this condition(Bearelly S et al. 2009). SD-OCT has been shown to be useful in
detecting some of these morphologic alterations (Fig. 27).
Hyperpigmented RPE areas (hypertrophy or hyperplasia) in OCT show a high reflectivity from the RPE with shadowing of the reflections from the choroid.
Fig. 27: Spectralis OCT shows a geographic atrophy (red arrow) in a patient with ARMD. Note the photoreceptor loss.
1.15.2 Neovascular ARMD
The neovascular (wet) form of ARMD is characterized by the overproduction of VEGF and the growth of abnormal vessels in the macular region. These vessels arise from the choroidal circulation and penetrate Bruch’s membrane to form a fibrovascular tissue beneath or above the RPE, or these vessels may arise primarily from the retinal circulation. The presence of VEGF and abnormal vessels leads to structural changes in the retina and choroid with the accumulation of fluid within the retina, in the subretinal space, or under the RPE. Furthermore, this neovascular invasion may lead to significant disorganization and remodeling of the retina, resulting in the loss of the RPE and photoreceptors with the formation of a disciform scar (Green WR, 1999).
OCT is very useful in detecting intraretinal, subretinal, or sub-RPE fluid. In patients with active neovascular ARMD, OCT imaging can be used to establish baseline retinal thickness, and determine the extent of neovascularization, fluid involvement, and other lesion components (blood, fluid, pigment, and fibrosis).
The growth of neovascularization is often accompanied by VEGF-dependent leakage from both the mature vessels and the growing immature vessels (Schuman JS, Puliafito CA, 2004). Choroidal
neovascularization is characterized by increased optical reflectivity of the RPE or disruption of the highly reflective band layer RPE/choriocapillaris
(Fig. 28). Intraretinal edema appears as an area of
low intraretinal reflectivity, which corresponds to intraretinal fluid accumulation and is consistent with an increased retinal thickness. Lipid exudation can also be present in patients with profuse intraretinal edema and appear as small hyper-reflective dots in the outer retina. The fluid may also accumulate in the space between the RPE and the neurosensory retina (Fig. 28).
Fig. 28: Spectralis OCT shows the presence of choroidal neovascularization (green arrow), intraretinal fluid accumulation (red arrow) and cystoid macular edema (blue arrow) in ARMD.
A pigment epithelium detachment (PED) demonstrates an elevation of the reflective band corresponding to the RPE/choriocapillaris complex and shadowing of the reflections returning from the deeper choroid. In contrast, neurosensory retinal detachment appears as elevations of the sensory retina above an optically clear space (Fig. 29).
Fig. 29: Spectralis OCT shows the presence of PED (blue arrow), and neurosensory retinal detachment that appears as elevations of the sensory retina above an optically clear space (subretinal fluid accumulation) (red arrow) in ARMD.
Disciform scarring and subretinal fibrosis are the end stage of CNV. The vascular components of CNV typically regress as the lesion becomes less active, and the fibrous components typically increase, resulting in disciform scar formation. Clinically the scar appears as smooth, elevated white or gray tissue in the subretinal space and on OCT imaging the scar corresponds to a highly reflective outer retinal or subretinal lesion
(Schuman JS, Pulliafito CA, 2004) (Fig. 30).
Fig. 30: Spectralis OCT shows the presence of disciform scarring (red arrow) as a highly reflective subretinal lesion between the retinal pigment epithelium and Bruch’s membrane.
1.16.3 Treatment of ARMD
There are several types of treatments for ARMD. Argon laser photocoagulation is a therapy for cases where the CNV is extrafoveal. Photodynamic therapy (PDT) is a cold laser irradiation to specifically destroy the neo-vessels, particularly
subfoveal CNV. The Anti-VEGF agents are drugs that bind to and block the activity of VEGF (Bandello F, Battaglia Parodi M, Siemerink MJ et al, 2010). Currently, the
intravitreal anti-VEGF application is the gold standard for the treatment of neovascular ARMD. The macular surgery is deserved for some complicated cases, such as large submacular hemorrhages in ARMD.
1.17 Anti-VEGF treatments
Even though the reasons and the clinic of these diseases are different, most of the vascular diseases of the retina and choroid are associated with exudative changes in the macula except epiretinal membrane. These changes are leading to damage of the photoreceptors and causing vision loss. New hopes in treating all of these diseases are the anti-VEGF therapy.
VEGF is a protein that occurs naturally within the body. Bodily tissues are thought to release this protein to signal the need for additional oxygen. Nearby blood vessels can sense the presence of this protein and in response, sprout and grow new blood vessels that extend into the VEGF releasing
tissue. This brings new pathways of blood supply into the oxygen needed tissue.
Many times the activity of VEGF is helpful, but for example after a CRVO, VEGF is thought to contribute to macular edema by increasing the permeability of the capillary walls, allowing fluids and proteins to make their way into the macular tissue. VEGF is also thought to be the culprit that stimulates the formation of the abnormal, fragile vessels of neovascularization.
Anti-VEGF agents are drugs that bind to and block the activity of VEGF (Bandello F, Battaglia Parodi M, Siemerink MJ et al., 2010).
1.17.1 Ranibizumab (Lucentis)
This is a recombinant humanized monoclonal antibody antigen-binding fragment (Fab) that neutralizes all known active forms of vascular endothelial growth factor A (VEGF-A), a protein that is believed to play a critical role in the formation of new blood vessels. Ranibizumab is an Anti-VEGF developed specifically for use in the eye. The usual dose of intravitreal injection is 0.5 mg in 0.05 ml.
Three main treatment strategies are currently adopted .The first strategy is a regular monthly injection that is the regimen adopted in initial major trials. Overall, around 95% of patients maintain vision regardless of lesion type, and 35–40% significantly improved, most markedly during the first 3 months. The second strategy is the three initial monthly injections followed by monthly review with re-injection when deterioration occurs as assessed by VA and OCT and the third strategy is the ‘treat and extend’ that administer three initial injections at monthly intervals and then gradually increasing the period between injections until deterioration is evident. If possible a tailored interval is determined for each patient. (Bandello F, Battaglia Parodi M, Schmidt-Erfurth U et al, 2010).
1.17.2Bevacizumab (Avastin)
This is a recombinant humanized monoclonal antibody that produces angiogenesis inhibition by inhibiting VEGF-A. In contrast to ranibizumab (48 kDa), bevacizumab is a complete antibody (149 kDa). The indication is macula edema and proliferative (neovascular) eye diseases, particularly for CNV in ARMD (Bandello F, Battaglia Parodi M, Schmidt-Erfurth U et al, 2010). The usual dose of intravitreal
injection is 1.25 mg/0.05 mL or 2.5 mg/0.1 ml.
According to the Comparison of Age-related Macular Degeneration Treatment Trials (CATT) study, there is no clinical significant difference or inferiority between ranibizumab and bevacizumab in treating patients with ARMD. (Martin DF et al., 2012). 1.17.3 Pegaptanib (Macugen)
Pegaptanib sodium was the first anti-VEGF agent approved by regulatory authorities for ocular treatment. Although offering visual outcomes superior to photocoagulation, the results are similar to outcomes with PDT, and use of pegaptanib is considerably less widespread than other anti-VEGF agents (Bandello F, Battaglia Parodi M, Schmidt-Erfurth U et al, 2010).
1.17.4 Aflibercept (Eylea)
Aflibercept is a novel VEGF inhibitor, with a high affinity for VEGF. It is a protein constructed by fusion of the second binding domain of the receptor VEGFR1 and the third binding domain of the receptor VEGFR2 to the crystalline portion of IgG1. This has resulted in aflibercept’s having a significantly higher affinity in vitro to VEGF compared with both bevacizumab and ranibizumab
(Holash J et al. 2002; Stewart MW, Rosenfeld PJ, 2008; Stewart MW,
2. Material and Methods
2.1 General objective:
Determine the agreement between the general ophthalmologist and retina specialist in the diagnosis and classification of macular diseases by high- definition spectral-domain optical coherence tomography (Spectralis OCT).
2.2 Hypothesis
Hypothesis (H1): There is statistically significant difference in agreement between the general ophthalmologist and the retina specialist to recognize findings by Spectralis OCT.
Null hypothesis (H0): There is no statistically significant difference in agreement between the general ophthalmologist and the retina specialist to recognize findings by Spectralis OCT.
2.3 Definitions
Degree of agreement: Is the concordance among raters. It gives a score of how much homogeneity, there is in the ratings given by judges.
Not in agreement: Is the discordance between raters.
Nongradable: No decision because of the poor image quality.
Limits of agreement: Refers to calculate the differences between each pair of observations of the two raters. The average of these differences is called bias and the reference range (mean + / - 1.96 x standard deviation) is termed limits of agreement.
2.4 Study population
After taken the approval by the Ethics committee das Institut für Klinische Epidemiologie und angewandte Biometrie der Eberhard Karls Universität zu Tübingen. We performed a retrospective chart review of patients who visited der Eberhard Karls, Universitäts-Augenklinik, Tübingen between August 2009 and September 2012. Clinical records of consecutive patients,
diagnosed with neovascular ARMD, BRVO, CRVO, BRVO, DME, and ERM that Spectralis SD-OCT examination with linear scan protocol were included in this study. In total, data of 500 patients were evaluated.
All patients underwent complete ophthalmic examination and Spectralis OCT. Fluorescein angiography and indocyanine green angiography were performed in some of the patients if needed. Using the digital chart system, list of the patients with predefined diseases were found.
2.5 Inclusion criteria
1. Patients with neovascular ARMD, BRVO, CRVO, DME and ERM.
2. Patients older than 18 years old.
3. Fundus photography and fluorescein angiography (except for eyes with ERM) at baseline.
4. Available Spectralis OCT examination of the macula.
5. Morphological abnormalities at the macula detected on the Spectralis OCT examination.
2.6 Exclusion criteria
1. Eyes having more than one disease affecting the macula (for example, neovascular ARMD and BRVO on the same eye).
2. The second eye of the included patients.
3. Eyes with poor quality of fundus photographs or fluorescein angiography.
2.7 Selection of the study population
After considering the inclusion and exclusion criteria, for each of the predetermined five diseases, 100 eyes of each disease were included into the analysis. All of the 500 consecutive eyes were selected by a senior ophthalmologist (FG) of the Department of Retina after checking the patient’s charts and Spectralis OCT scans.
Eyes were selected if morphological abnormalities at the macula were seen on the Spectralis OCT examination.
2.8 Design
This study is transactional, correlational, and retrospective; because we analyze significant morphological findings (variables) that are presented in each disease into a single image at a time, also the relationship that exists between intra and interobserver.
2.9 Design description.
In September 2012, images (vertical and horizontal linear scans do Spectralis OCT) of the patient's first visit were selected by the general ophthalmologist (examiner 1). By that time the central retinal thickness (CRT) was measured in both images, determining the average value of the 500 eyes of 500 patients with the diagnosis categories noted above. After that the variables of the 5 groups were assessed, in addition to assessing the quality of the image by the OCT.
Between September 2012 and December 2012, the general ophthalmologist learned to use the Spectralis OCT in high resolution as well as, interpret and diagnose macular disorders during the clinical routine.
In December 2012, the second measurement of the CRT was repeated by the same general ophthalmologist; the same OCT image-scans were used as before.
In March 2013, the retina specialist (examiner 2), with an experience of performing and analyzing of the Spectralis OCT evaluated the CRT as well as the variables of the included eyes.
2.10. Sample size
For the analysis, we included into the study 500 images of 500 eyes (500 patients) with predefined macular diseases.
These were:
1- 100 eyes (100 patients) with age-related macular degeneration (ARMD).
2- 100 eyes (100 patients) with branch retinal vein occlusion (BRVO).
3- 100 eyes (100 patients) with central retinal vein occlusion (CRVO).
4- 100 eyes (100 patients) with diabetic macular edema (DME).
5- 100 eyes (100 patients) with epiretinal membrane (ERM).
2.10.1 Analyses of the OCT scans
In all patients, the macula was scanned in the horizontal and vertical meridians using the standard lineal protocol of Spectralis OCT. The CRT was calculated for each image using a 5mm length centered through the fovea, twice by general ophthalmologist (HT), in September 2012 and December 2012 and thereafter by the retina specialist (ML) in March 2013.
Data was obtained from the right eyes if both eyes fulfilled the inclusion criteria.
2.11 Evaluation method
2.11.1 Ophthalmologic examination
All patients had a general ophthalmological examination including best corrected visual acuity, biomicroscopy of the anterior segment, measurement of the intraocular pressure and fundoscopy in mydriasis. All eyes had color fundus photography and Spectralis OCT. Fluorescein angiography and Indocyanine green angiography was performed if needed.
2.12 Examination protocol of the OCT
2.12.1 Preparation of the patient
After the eye examination, OCT was performed on patients with suspected macular alteration.
1- Patient data was given. 2- Pupillary dilation.
3- Positioning of the head of the patient (Supported of the front and chin). 4- IR+OCT of Spectralis.
Spectralis OCT examinations were performed by an ophthalmologist or technician.
2.12.2 Preparation of the OCT
OCT scans included in this Study were generated using Heidelberg Engineering, HTR-OCT Spectralis, and version 1.8.6.0. Heidelberg, Germany (Fig.31)
Fig. 31: Spectralis OCT (Heidelberg Engineering, Heidelberg, Germany).
2.12.3 Settings of Spectralis OCT
Eye: OD/OS Angle: 0-90 grades Focus: -10 to10 Diopters Sensibility: >59
Power: IR 100% Rate: 4.7 sec.
Resolution: High resolution Application structures: Retina Scan: Horizontal or vertical
ART: 100 Frames A-Scans: 1024 to 1536
Fig. 32: Spectralis OCT horizontal line scan shows the layers of the retina and measurement of CRT. ILM: internal limiting membrane; NFL: nerve fiber layer; GCL: ganglion cell layer; IPL: inner plexiform layer; INL: inner nuclear layer; OPL: outer plexiform layer; ONL: outer nuclear layer; ELM: external limiting membrane; IS/OS: photoreceptor inner/outer segment junction; RPE: retinal pigment epithelium.
Fig. 33: Spectralis OCT vertical line scan shows CRT measurement from ILM to RPE/Bruch membrane complex.
The CRT was manually measured in all scans using the manual caliper tool built into the OCT software
(Fig. 32, 33) twice by HT, in September 2012 and
December 2012 and again by ML in March 2013. Both examiners were masked to any clinical, angiographic or functional status of the eyes when grading the scans.
CRT was defined as the interface between the dark vitreous and the bright reflection of the internal limiting membrane (ILM) and the outer retinal surface of the bright retinal pigment epithelium/Bruch’s membrane complex at the fovea. Measurements were taken in the central 1mm of the OCT scans (Ian C, Han MD, Jaffe GJ, 2008) (Fig. 32, 33).
In addition, all OCT scans were graded for the presence or absence of the following morphological findings: foveal depression, epiretinal membrane, vitreofoveolar traction, pseudocyst, splitting, verticalisation of the foveal edge, macular hole, pseudomacular hole, lamellar macular hole, neurosensory detachment of the retina, retinal pigment epithelium detachment, external limiting membrane, photoreceptors inner and outer segments.
2.13 Artifacts and Gradability of the images
Each horizontal and vertical line scans were reviewed in terms of the gradability. Scans with significant image artifacts resulting in reliable thickness measurements of the retina were excluded. Reasons for scan exclusion included weak saturated scans where the boundaries of the retina or intraretinal morphology could not be identified adequately and off-center scans which were not centered within the foveal pit.
For patients with multiple acceptable scans per eye in the same clinic visit, one scan per eye was chosen at random to be included in the study.
2.14 Color fundus photography, Fluorescein angiography and Indocyanine green
angiography
All patients had color fundus photography of both eyes. Some patients underwent fluorescein and indocyanine green angiography at the first presentation to diagnose the macular pathology. These examinations were performed by skilled photographers at the imaging department.
